Chipping Blade

R

rincan

Joined
Aug 20, 2014
Messages
57
I finished making a knife from a file, I heated the file to non-magnetic let it slowly cool to soften the metal and then heated it up once more to bend the file slightly and give the blade a slight curve then shaped the blade with hand files and some grinding. When the blade was the shape i wanted it i heated it up to non-magnetic again and quenched in warm motor oil. I tempered in the oven for about 45 min to an hour at around 450 till brownish, then let it cool and tempered again at 475 till brown and let it cool. In the end the blade looked good but i am having one small problem. The blade is chipping and i cannot get a smooth sharpening. The blade is sharp but it has fairly large chips all down the cutting edge.

I dont know if this matters but I heated the blade up in a small homemade propane forge.

Anyone have any suggestions as to what I did wrong?
 
It sounds to me like you may have grain growth caused by overheated the blade. My first knives were like this. If you are willing to learn from this, break the knife and see what the grain looks like. Otherwise you can use it and let it possibly break on its own, then examine it. You want the grain to look smooth like broken flint rather than sand.
Jason
 
It shouldn't be chipping after 450, so something isn't right.

Good pictures would be helpful. The untrained eye can sometimes have trouble differentiating chipping from roll.
 
ok i think i got the picture to work for you guys! jawilder sounds good i think ill break it to find out but is there a way to shrink the grain by any chance incase it happens again?
 
I don't see much "large" chipping in the photo.

Causes may be:
Too low an edge angle - Re-sharpen the edge at a higher angle, like 15-17° per side. Try this first and see if it solves the problem.
Poor HT - There is a lot in your HT that could be improved. Oil is wrong type. Heating method may be poor, etc.
Steel choice - You have no idea what the steel type is, so you have no idea what the HT parameters should be.
Grain growth caused by too high a temperature or too long at high temperature. Breaking the blade is the only way to know if this was the problem. If sharpening at a higher angle doesn't solve the problem, then a destructive test ( breaking the blade) is called for.

BTW, what oven type was used for the tempering, and how was the 450F and 475F temperature determined?
 
rincan, where in Alberta are you? If you are relatively close I can help you out. There is a great supplier in central Alberta, and you can get a piece of 1084 for peanuts with shipping that rarely takes more than two days. (Knifemaker.ca)
 
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